The invention relates to a medium voltage electrical switch with an elongated vacuum cartridge, housing a pair of contacts extending axially inside the cartridge. One contact is movable, axially slidable. The cartridge is sealed off at its ends by base plates, at least one of which is metal and comprises a center part electrically connected to one of the contacts, a current input strip arranged on the periphery of the base plate, a coil mechanically and electrically united to the base plate and connected between the strip and the center part of the base plate to form a circuitous current flow path which generates an axial field in the contact separation zone.
U.S. patent application Ser. No. 07/668,162 (now U.S. Pat. No. 5,515,315) filed by applicants describes an electrical switch of the kind mentioned in which current breaking is performed in the vacuum cartridge. The axial magnetic field generated by the current flowing in the coil increases the breaking capacity of the cartridge by causing diffusion of the arc and preventing any concentration of energy at a particular point. This coil is coaxial to the cartridge and flattened in shape, and it can be formed either by a conductor fixed by welding to the base plate, or be defined by a spiral groove cutout of the bulk piece, i.e. out of the thickness of the base plate on the internal face of the cartridge.
This state-of-the-art switch gives satisfaction but it has proved of interest to increase the intensity of the axial magnetic arc blowout field, and the object of the present invention is to achieve such an increase while preserving the simple structure of the cartridge.